Process for the photomechanical manufacture of printing forms for intaglio printing



Patented May 23, 1939 raocnss ron THE rno'romncnamcan- MANUFACTURE OFPRINTING FORMS FOR INTAGLIO PRINTING Josef Giirig, Loev'enich, nearCologne, Germany,

. assignor to firm Bekk & Kaulen Chemise-he Fabrik G. in, b. 11.,Loevenich, near Cologne, Germany I No Drawing. Application March 4,1936, Serial No. 87,068. In Germany April 2, 1935 Claims; (01. sis-5.7)

a The usual procedure for the manufacture of printing forms for intagliocopperplate printing and the like working with a doctor consists infirst copying the: image to be reproduced on a "light sensitive carbontissue, whereupon the produced copy is transferred by da'bbing 'to the fprinting form and is treatediand etched here in the customary way.Butthe use of the carbon tissue for the manufacture of deeply etchedprinting formshas the disadvantage, that this paper'is' very; sensitiveagainst atmospheric influences, and this is most unfavourable especiallyin the manufacture of'polycolour reproductions.

Since the carbon tissue changes most easily its shape and especially itssize under the influence of weathering, there is always danger that thetransferred 'image proves to be larger for one easily become unsuitable,particularly for quality work. It is from this reason that till now byintaglio copperplateprinting generally only reproductionsin one colourwere manufactured.

} Coloured reproductions are mostly printed only {Jon small machines oneup, so that the whole printing cylinder may be slided and rocked tillthe mono-coloured images will fit correctly on one another. But whenlarger sizes are used, it

is not possible to handle the printing cylinder in xsuch a manner,thatthe single impressions or images may bebrought to fit on one anotherexactly. l

This drawback is eliminated by the procedure according to the presentinvention. For this purpose no carbon tissue at all is usedhere, but

the metallic support utilised for theprinting form '(plateQcyIinderorthelike) is coated with l copied at the same' time upon the light sensitive.layer of the printing form. When image and screen are transferred tothe base of the printing form by exposure to light, the treatment withan etching solution is performed in accordance to the present invention.Preferably such etching solutions are used, which, besides the usualmordant, like ferric chloride, contain an acid of such a kind, as forinstance lactic acid or the like, which attacks or penetrates and swellsthe not hardened colloid layer but does not corrode or attack the metalof the plate or the like. There is no need in this case to coat withbituminous varnish the places not to be etched, since the hardened partsof the colloid layerare thoroughly proofagainst the mordant.

It further has been proved, that not rarely difllculties are met inobtaining useful prints from the printing forms produced by the presentmethod, and that these difficulties are due to an insuflicient ordefective formation of the edges for supporting the doctor. It has beenfound that the imperfect formation of these edges was I ing to thepresent method, the very time and degree of exposure which is thoroughlysuiiicient to produce the edges for supporting the doctor in the formercase, frequently does not suflice to accomplish with certainty thoseedges on the printing form in the process of the present invention.

This observation may be accounted for in the following manner: Whenworking with carbon tissue those parts of the light sensitive layerwhich originally were on the top. side of the paper lie underneath, i.e. in direct touch with the metallic support when the sensitive layer isdabbed to the latter. Now as at the surface of the layer the hardeningisnaturally greatest when thesensitive layer is exposed in order to copythe screen, there is full security that the strongestly"hardened partsof the layer are brought into immediate contact with the me-' tallicsupport of the printing form when said layer is dabbed on the metal.Consequently one can be sure that on developing and etching the screencopy to produce the edges for supporting the doctor or the like, theseedges willaperfectly appear on the metallic printing form, no matterwhether the exposure .has been a short or a longer one.

But things are different, if according to the present invention the halftone image and the screen are transferred directly to a light sensitivelayer which has previously been arranged on the metallic support. For inthis casethat part of the layer which by exposure is hardened most lieson the top, whereas the least hardened part lies on the underside, i. e.in contact with the metallic support. Now, if the exposure in copyingthe screen is not long enough, it may happen that in developing andetching'the light sensitive layer, the developing and etching meansintrude laterally through the non-exposed parts of the surface beneaththe superficially hardened parts of the edges produced by copying'thescreen. Then the latter are removed when the parts of the layer whichhave remained unexposed are dissolved or removed, and thus the edges forsupporting the doctor will no more be formed in a satisfactory mannerwhen the metal form is etched.

. Accordingly, when the screen is copied 'on the sensitive layer of themetal form it is important for the process of the present invention toexpose during such a time that there will be perfect security, that theexposed spots of the sensitive layer are thoroughly hardened down to thebasis. i. e. to the surface of the metal form. If the exposure has beenso lengthened in this way, the same reliability will exist here for thecompletion of the edges as with the pigment paper process, and thereforeperfect prints then are to be obtained here also with certainty.

It may easily be ascertained, if needed by a preliminary test, what timeof exposure will be required toattain the desired aim in any par ticularcase. By using a given source of light and a sensitive layer of definitecomposition and sensibilisation, and of given thickness one mayascertain what time is wanted in order to arrive at a perfect completionof the edges for supporting the doctor on the metallic supportbyetching, if the screen is copied alone, i. e. without the half toneimage. In this direction experience has shown what follows:

With the pigment paperprocess the time, for copying thescreen should belonger by about one quarter of the time required for copying the halftone image, say for instance 8 minutes for. the screen against 6 minutesfor the half tone image. -Now, all other things being equal, it hasproved .suitable, when using the process of the present invention, toexpose for the copying of the screen about thrice as long as for thecopying of the half to'neimage, say for instance about 18 minutesagainst 6 minutes.

The process according to the present invention may be executed indifferent ways andmanners. The layer of the light sensitive colloid mayconsist of a chromatised glue. soluble in warm water, like thechromatised so-called Beka. photoengraving glue (as manufactured byMessrs. Dr. Bekk 8: Kaulen Chemische Fabrik G. m. b. H., of Loevenich,.near Cologne), or chromatised gum arable. After the screen and thediapositive or the like are copied on this .only to a relatively lowdegree.

layer by exposing them, the one after the other, during the timerequired in accordance to what has been said above, the etching solutionis brought on the plate or the like without previous development.Preferably the etching solution in this case is composed in such a way,that is to say it shall suitably have such a viscosity, that the copyinglayer, even if not exposed to the light, would not be influenced by theferric chloride solution as such, but that the added weak acid attacksand penetrates those parts of the colloid layer, which are not hardenedat all or As an etching solution adapted for this purpose may be taken aferric chloride solution of 48-50 B with an addition of 3-5% lacticacid.

When those parts of the colloid layer which were not exposed at all oronly in a relatively small measure are brought to swelling by the lacticacid, the ferric chloride can act at the penetrated spots on the metalof the printing form, whereas the weak acid itself neither does nor needcorrode the metal. The copying or colloid layer is brought to swellingby this acid of course in such a. way that those image spots which wereexposed least are attacked first, and

that the further swelling of the layer takes place ones, which aresuited to cause the nonhardened parts of the colloid layer to swell, butto leave unattacked the hardened parts and which do not attack atall oronly to a small degree the metal of the form.

After the treatment with the acidulated mordant, if necessary, atreatment with an etching bath of the usual kind, for instance a ferric.

chloride solution of appropriate concentration, may take place. When theetching procedure is finished, the printing form is freed from' theinstead of the chromatised glue or gum soluble in warm water asmentioned above, a layer of chromatise'd gelatine may be employed whichis produced by means of the unchanged gelatine as it is on sale andwhich quickly sets and only swells in warm water without dissolving. Inthis case the image after having been; transferred to the chromatisedlayer in an adequate manner and after the latter having been screened byexposure may first be developed 'in water. The temperature of thedeveloping water, however, then ought to be such, that the gelatine isnot dissolved even at the spots not exposed to the light andconsequently not hardened, but.

(edible gelatine), for this reason a temperature of 40-45 C. should notbe substantially exceeded. Since the gelatine is not dissolved by thewater Performing the development, after the completlon of the latter thegelatine will yet be present on the plate as an apparentlyuniformuninter-' rupted layer. During the'subsequent etching those parts of thegelatine layer, which were unexposed or less exposed and made to swellby the development, are more readily penetrated by theimordant than theparts hardened more or less. This even then will be the case if only thenormal mordants are used, such as ferric chloride solution withoutaddition of any acid. In this case, therefore,only those normal mordants'need be used. According to the lessor greater degree ofhardeningcf the respective spots the mordant will penetrate morequicklyor more slowly through the gelatine layer to the metal and will efiectherethe correspondingly graduated etching. .After etching the gelatinelayer may be removed in a corresponding manner as in the proceduredescribed before.

It has been found to be suitable in this second named form of executionof "the new process to add a finely divided filler to the gelatinebefore the latter isspread over the metal plate or the like. By means ofthe filler on the one hand the rapid setting of the gelatine when spreadby whirling or the like over the plate or the like may be delayedwhereby the formation of a uniform layer is facilitated. n the otherhand the deep etching may be favourably influenced thereby, as thefiller will be washed out during the development preferably or'only fromthose spots of the layer which are hardened not at all or only a little.As the degreeof hardening and of swelling dependent thereupon may be,more 3 or less of the filler will be washed out of a certain partofthegelatine layer. The latter, however, will be more readily penetratedby the etching means at the spots more freed from the filler than atthose places, which retain still more or all of it. Thus the gradationof the tone in the etched image will be furthermore influencedfavourably.

ing of the latter on the metal plate, therefore pct being settledtoorapidly.: Preferably as. fillers pigments may be used, I. i. the redpigment of Messrs. H. Schmincke 8; Co., of Dusseldorf. ,The use of suchpigmentsyet offers theparticular advantage that at the same time acoloration of the gelatine layer is, caused and therefore the inspectionof the developed gelatine image is facilitated, as during thedevelopment more or less of thepigment is dissolved out of, the parts ofthe layer hardened not or ,less. For instance a cleaned copper plate maybe coated for this purpose in the whirler with a copying mixturecomposed of 1000 mm of water, 120 gr. of edible gelatine, 100 com. ofBeka photoengraving glue,

and 100 gr. of a red body-colour. This solution or mixture maybesensibilised with equal 'parts of ad%asolution of potassiumbichromate. The addition of the, glue to the gelatine here also isintended to prevent too rapid a setting of the gelatine on the plate,and thus to facilitate the formation of a thoroughly uniform film orlayer.

i After the plate or the like is exposed under the diapositiveor thelike and under the screen during the required time, the development iscarried out. For this purpose the plate is suitably first put into warmwater where it is left, for instance,

for about two minutes. Then it is brought into a dyeing and hardeningbath, which for instance hardened gelatine is to be found.

may consist of 1000 ccm. of water, 20 to 30 gr. of water-soluble anilinedye, like methyl violet, and 40 to 50 gr. of alum. After some minutesthe plate is taken out of this bath, and the development then isfinished in warm water. The used water soluble aniline dye also servesthe purpose to facilitate the examination of the developed image or ofthe degree of development reached, since during the final development inwarm water this'dye is washed out or away from those places where theunhardened swollen or relatively little It is selfexplanatory that thedyeing with aniline dye, if desired, may be employed also where nofiller like a pigment was added to the colloid solution. The tanningagent, f. i. alum, added to the middle bath confers to the layer thenecessary stability during etching and contributes furthermore topromotethe gradation of the latter according to the tone values of theimage or picture. Instead of alum any othersuitable tanning agent maybeused, f. i. formaline or the like. There is no need to treatwith thetanning means in the same bath as with the dyeing solution, but they maybe effected independently from one another. Also, the treatment with thetanning agent or with the dyeing solution, or with both agents may beomitted. On the other hand the tanning may be combined with the etchingby adding the tanperformed in the otherwise usual way, for instance withferric chloride solution of varying composition and concentration. Inthis case, of course, the etching may be performed under full daylight,in contrast to the first example of execution where the undevelopedimage was to be etched. After the etching is finished, first the varnishis removed and then the remaining copying layer, if desired by means ofwater and emery powder or the like.

The process according to the present invention is suited in first linefor the manufacture of planographlc intaglio printing forms, but'it mayalso bev employed for the'manufacture of rotary intaglio printing forms.As metal for the plates or the like, copper is the most important, butin certain cases other metals, such' as brass, zinc or aluminum mayalso-be employed.

Having now particularly described and ascertained the nature of my saidinvention, I declare that what I claim is:

1. A. process for the photomechanical manufacture of printing forms forintaglio printing by means of a doctor which comprises covering ametallic body used as the basis for the printing form with a lightsensitive chromatized colloid layer, exposing the same twice, under adiapositive of a continuous unscreened half-tone image and under aphotogravuro screen in any succession, the one after the other, and thentreating said metallic body coyered with the undeveloped, twice exposedcolloid layer with a swelling means and. an etching means.

2. A process for the photomechanical manufacture of printing forms forintaglio printing by means of a doctor which comprises covering ametallic body used as the basis for the printing form 'with a lightsensitive chromatized colloid layer, exposing the same tWice under adiapositive of a continuous half-tone image and under a photogravurescreen in any succession, the one photogravure screen being" made for alonger period than that independently made for copying the continuoushalt-tone image and for such a time, that those parts of the sensitivelayer the,

surface oil which is directly met by the light during the copying of thephotogravure screen are. hardenedwith certainty down to the base oi saidsensitive layer, and thereafter treating'saidmetallic body with theundeveloped, twice exposed colloid layer with a swelling means and anetch-. ingmeans. l

I 3.. A process for the photomechanicalmanuiac-ture of printing-formsforintaglioprinting by meansof a, doctor which comprises covering" ametallic body used as the basis for the printing form with a layer ofgelatine of .thetrade of such a kind which only will swell on beingtreated with warm. water without dissolving and which is rendered lightsensitive by chromatizing exposing said sensitive layer twice, under adiapositive of a'continuous'halI-toneimage and under a photogravurescreen-in any succession, the one 1 after the other, then treating saidtwice exposed gelatine layertwlth water ot such a temperature,

that the gelatine is not dissolved even at the unexposed spots butisonly caused to swell at said spots, and thereafter subjecting saidprinting form to. the action oif an etching means.

4. A process for the photomechanicalmanufacture of printing formsforintaglio printing by means ot a doctor which comprises covering ametallic-body used as the basis forthe printing form with alightsensitivechrornatized colloid layer, exposing the same twice, under adiaposi- 1 tive of a continuous half-tone'imageand under a photogravurescreen inanysuccession, the one after theother, and 'then tre'ating'said metallic body with the undeveloped, twice exposed colloid layersimultaneously with swelling-etching means, said means consisting. of amixture of an etching salt and a weak organic acid, said organic'acid,

layer,exposingj the same twice, under a diaposi tive of a continuoushalf-tone image and under a photog'ravure screen in any succession, theone after the other,'-andthen treating said'metallic body with theundeveloped, twice exposed colloid layer. simultaneously withswelling-etching means, saidf'means consisting of a' mixture of anetching salt and lactic acid. r

6., A process for the 'phot'omechanical manufacture of printingforms forintaglio printing by means of adoctor which comprises covering ametallic body used as'the basis for the printing form with a lightsensitive chromatized colloid layer, exposing the sametwice, under adiapositive of a continuous halt-tone image and under 1 aphotogravurescreen in any succession, the one after the other, and then treatingsaid metallic body with the undeveloped, twice exposed colloid layersimultaneously with swelling-etching means, saidmeans consisting of amixture of ferric chloride and lactic acid. I 7. A process for thephotomechanical manufacture of printing forms ,ior intaglio' printing bymeans of a doctor which comprises covering a metallic body used as thebasis for the printing i'orm with a layer of gelatine of the trade ofsuch a kind which only will swell on being treated with warm waterwithout dissolving and which is rendered 'light sensitive by.chromatizing, exposingsaid sensitive layer twice, under a diapositive ofa continuous half-tone image and undera photogravure screen in anysuccession, the one after the other, then treating said twice exposedgelatine layer with water of such a temperature, that the gelatine isnot dissolved even at the unexposed spots but is only caused to swell atsaid spots, and thereafter subjecting said printing form to the actionof a ferric chloride solution.

8. A process for the photomechanical manuiacture ofprinting forms forintaglio printing by means of a doctor which comprises covering ametallic body used as the basis for the printing form with a layer ofgelatine of the trade of -such a kind which only will swell on beingtreated with warm water without, dissolving and which is rendered lightsensitive by chromatizing, exposing said sensitive layer twice, under adiaposi- "tive of a continuous half-tone image and under a photogravurescreen in any succession, the one after the other, then treating saidtwice exposed gelatine layer with water of such 'a temperature, that,the gelatine is not dissolved even at the qunexposed spots but is onlycaused to swell at saidspots, dissolved dyes, being added during thistreatmenhthen removing said dyes again from the unexposed spots of saidgelatine layer by an after-treatment with water, and thereafter bringingan etching means on said treated gelatine layer, said etching meanspenetrating the previously swelled parts of said gelatine layer andetching the parts of said metallic body beneath said swelled gelatineparts.

9. A process for the photomechanical'manu facture of printing forms forintaglio printing by means of a doctor which comprises covering ametallic body used as the basis for the printing form with a layer ofgelatine of the trade of such a kind which only will swell on beingtreated with warm water without dissolving and which is rendered lightsensitive by chromatizing, ex-

posing said sensitive layer twice, under a diapositive of a continuoushalf-tone image and under a photogravure screen in any succession, theone after the other, then treating said twice exposed gelatine layerwith water of such a-temperature,

that the gelatine is not dissolved even at the unexposed spots but isonly caused to swell at said spots, dissolved dyes and a tanning agentbeing added during this treatment, then removing said dyes again fromthe unexposedspots of said gelatine layer by-an' after-treatment withwater, and thereafter bringing an etching means on said treated gelatinelayer, said etching means penetrating the previously swelled partsofsaid gelatine layer and etching theparts'of said metallic body beneathsaid swelled gelatine parts. a

10 Aprocess for the photomechanical manui'acture of printing forms forintaglio printing by means of a doctor which comprises covering ametallic body used as the basis for the printing form with a layer ofgelatine of the trade of such a kind which only will swell on beingtreated with warm water without dissolving and which is renderedlight-sensitive by chromatizing, ex-

posing said sensitive layer twice, under a diapositive of a continuoushalf-tone image and under a 'plfotogravure screen in any succession, theone after the other, the exposure for copying thephotogravure screenbeing made for a longer period than that independently made for 'copyingthe continuous half-tone image and for such perature, that the gelatlneis not dissolved even a time, that those parts of the sensitive layer,at unexposed spots, but is only caused to swell at the surface of whichis directly met by the light said spots, and thereafter subjecting saidprintduring the copying of the photogravure screen, ing form to theaction of an etching means.

are hardened with certainty down to the base of said sensitive layer,then treating said twice exposed gelatine layer with water of such atem- JOSEF some.

